1. Technical Field
The present invention relates to a fan controlling circuit for detecting rotational speed of a fan.
2. Description of Related Art
Developments in today's highly information-intensive society have led to remarkable improvements in performances of electronic devices. During operation of many contemporary electronic devices such as central processing units (CPUs), large amounts of heat are produced. Typically, an electric fan is used to facilitate removal of the heat. The fan must run stably, so as to prevent the device from becoming unstable or damaged. A controlling circuit accompanying the fan is important to ensure the fan is running normally. Unfortunately, noise signals interfere with rotational speed signals of a typical fan controlling circuit.
Therefore, a new fan controlling circuit for detecting rotational speed of a fan is desired to overcome the above-described deficiency.